How to Kill a Frozen Process

Prerequisites

Before killing a process, make sure you have:

• SSH access to your VPS
• Root or sudo privileges
• The Process ID (PID) of the frozen application

Step 1: Identify the Frozen Process

First, find the Process ID (PID):

top

Or:

ps aux | grep "process-name"

Example - find a frozen Apache process:

ps aux | grep apache2

The second column is the PID (e.g., 12345).

Method 1: Using kill (Gentle Termination)

Send SIGTERM signal (default) - allows process to clean up:

kill PID

Example:

kill 12345

With explicit SIGTERM:

kill -15 PID

Method 2: Using kill -9 (Force Kill)

If gentle kill doesn't work, force kill immediately:

kill -9 PID

Example:

kill -9 12345

Method 3: Using pkill (Kill by Name)

Kill all processes with a specific name:

pkill process-name

Example:

pkill nginx

Force kill by name:

pkill -9 nginx

Method 4: Using killall (Kill by Exact Name)

killall process-name

Example:

killall apache2

Method 5: Kill from top/htop Interactive

In top:

1. Press k
2. Enter the PID
3. Enter signal (15 for gentle, 9 for force)

In htop:

1. Select process with arrow keys
2. Press F9
3. Select SIGTERM (15) or SIGKILL (9)
4. Press Enter

Understanding Kill Signals

Most common signals:

• SIGHUP (1) - Reload configuration
• SIGINT (2) - Interrupt (like Ctrl+C)
• SIGTERM (15) - Terminate gracefully (default)
• SIGKILL (9) - Force kill immediately
• SIGSTOP (19) - Pause process
• SIGCONT (18) - Resume paused process

Kill All Frozen Processes of a User

pkill -u username

Force kill all user processes:

pkill -9 -u username

Kill All Processes Except Specific Ones

Kill all except your SSH session (advanced):

kill -9 -1

Check if Process is Still Running After Kill

ps aux | grep PID

Or:

kill -0 PID

Returns success if process exists.

Common Scenarios

Apache/Nginx is frozen:

systemctl restart nginx

Instead of killing individually.

MySQL not responding:

systemctl restart mysql

User program frozen (like Python script):

pkill -f "python script.py"

Automatically Kill High-Memory Processes (Monitor Script)

#!/bin/bash
MAX_MEM=80  # 80% memory usage
MEM_USED=$(free | grep Mem | awk '{print ($3/$2) * 100}')
if (( $(echo "$MEM_USED > $MAX_MEM" | bc -l) )); then
    ps aux --sort=-%mem | head -5 | awk '{print $2}' | xargs kill -9
fi